The present invention relates to a polyester resin composition which is suitable as adhesives, paints and various coating agents and has excellent adhesive property and setting property to various kinds of raw materials.
A combination of polyester resin with amino resin such as melamine resin, urea resin and benzoguanamine resin has a thermosetting property and has been used as various paints and coating agents. A combination of polyester resin with phenol resin usually has a poor setting property as compared with the above-mentioned combination and lacks in a multipurpose property.
A thermosetting resin such as melamine resin, urea resin, benzoguanamine resin and phenol resin is set when methylol group caused by formaldehyde and an alkyl-etherized product of methylol group are made to react with hydroxyl group and carboxyl group at the terminal of the polyester resin in the presence of acidic catalyst.
Melamine resin, urea resin, benzoguanamine resin or phenol resin is able to conduct a self-cross-linking but, when the terminal of polyester is a reactive point, the cross-linking density lowers as the molecular weight of the polyester increases. Therefore, the characteristic feature caused by the cross-linking is not improved significantly.
In the setting of polyester resin, there are many cases where the terminal hydroxyl group and carboxyl group are the reactive points. In that case, the cross-linking density lowers when molecular weight of the polyester increases. The characteristic feature caused by the cross-linking is not improved significantly. In addition, a combination of the polyester with the phenol resin has a poor setting property and lacks in multipurpose property.
An object of the present invention is to provide a polyester resin and a composition thereof which has a reactive point other than hydroxyl group and carboxyl group and which is able to set with melamine resin, urea resin, benzoguanamine resin or phenol resin based on the reactive point.
The present inventors have carried out an intensive investigation for the setting reaction of polyester resins and achieved the present invention. Thus, the present invention is a composition which is characterized in that the composition contains a polyester resin containing 50 equivalents/ton or more of an aromatic ring having a phenolic hydroxyl group and having no substituent at ortho- and/or para-position(s) to the said phenolic hydroxyl group in the resin and also contains at least one member selected from melamine resin, urea resin, benzoguanamine resin and phenol resin.
The present invention utilizes an electrophilic substitution reaction of a phenol ring at ortho- or para-position.
Although the polyester resin of the present invention may have a hydroxyl group or a carboxylic acid group utilized as a reactive point as before, it always contains a phenol ring. With regard to a material for introducing a phenolic hydroxyl group into polyester, there is exemplified a compound which has a hydroxyl group and/or a carboxylic acid group for forming an ester bond and has an aromatic ring having a phenolic hydroxyl group and hydrogen atom at least at one of ortho- and para-positions to the said phenolic hydroxyl group. Examples of the specific compound thereof are diphenolic acid, p-hydroxybenzoic acid, p-hydroxyphenylacetic acid, p-hydroxyphenylpropionic acid, p-hydroxyphenethyl alcohol and 5-hydroxyisophthalic acid. Among them, diphenolic acid and p-hydroxyphenylacetic acid are preferred in view of the reactivity.
The polyester of the present invention contains 50 equivalents/ton or more of an aromatic ring which has a phenolic hydroxyl group and where at least one of ortho-position and para-position to the phenolic hydroxyl group is hydrogen atom in the resin. When it is less than 50 equivalents/ton, concentration of the reactive point may be too low whereby the cross-linking density may not be able to be increased.
Content of the aromatic ring is preferably 70 equivalents/ton or more and, more preferably, 80 equivalents/ton or more. Although its upper limit is selected depending upon the required characteristic and is not particularly limited, it is preferably 5,000 equivalents/ton or less, more preferably 3,000 equivalents/ton or less and, particularly preferably, 2,000 equivalents/ton or less.
With regard to the dibasic acid component of the polyester resin, there are exemplified aromatic dibasic acid such as terephthalic acid, isophthalic acid, o-phthalic acid and naphthalenedicarboxylic acid; aliphatic dicarboxylic acid such as succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid and dimeric acid; and alicyclic dicarboxylic acid such as 1,4-cyclohexanedicarboxylic acid and 1,3-cyclohexanedicarboxylic acid. With regard to the glycol component, there are exemplified ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, 2-ethyl-2-butyl-1,3-propanediol, diethylene glycol, 1,4-cyclohexanedimethanol, an adduct of bisphenol A with ethylene oxide, an adduct of bisphenol A with propylene oxide and polyether glycol such as polyethylene glycol, polypropylene glycol and polytetramethylene glycol.
Further, a lactone such as xcex5-caprolactone and xcex4-valerolactne and an oxycarboxylic acid such as p-hydroxyethoxybenzoic acid may be used as a material for the polyester resin as well.
It is also possible to jointly use trifunctional and higher functional components such as trimethylolpropane, pentaerythritol and trimellitic acid anhydride. It is particularly preferred to jointly use a trifunctional or higher functional component so as to abundantly incorporate a compound having one carboxyl group or hydroxyl group in a molecule such as diphenolic acid, p-hydroxyphenylacetic acid, p-hydroxyphenylpropionic acid or p-hydroxyphenethyl alcohol into a polyester resin.
With regard to a number-average molecular weight of the polyester resin of the present invention, it is preferred to be 3,000-50,000 and, more preferably, 5,000-30,000. When the said molecular weight is less than 3,000, the toughness of the coat may be poor while, when it is more than 50,000, viscosity of the solution may be high and inconveniences in the operation may be significant.
In the present invention, at least one member of thermosetting resin selected from melamine resin, urea resin, benzoguanamine resin and phenol resin is jointly used. A specific example is a compound containing a methylol group prepared by the reaction of a melamine, urea, benzoguanamine or phenol compound with formaldehyde or paraformaldehyde etc.
The methylol group may be etherified with an alcohol having 1-6 carbon atom(s). It is preferred that the ratio of polyester resin to thermosetting resin used is within a range of 5-100 parts by weight of the thermosetting resin to 100 parts by weight of the polyester resin.
In the present invention, it is preferred to add a catalyst for setting during the setting treatment so as to improve the setting property. With regard to the catalyst for setting, there are exemplified sulfuric acid, p-tolenesulfonic acid, dodecylbenzenesulfonic acid, naphthalenesulfonic acid and an amine block substance where all or a part of the above is neutralized with an amine compound. Although amount of the catalyst for setting to be added varies depending upon the conditions for setting treatment, etc., it is preferred to be within a range of 0.01-0.5 part by weight for 100 parts by weight of the polyester resin.
In the polyester and a composition thereof according to the present invention, there takes place a setting with a good efficiency due to an electrophilic substitution reaction by a methylol compound at ortho-position or para-position of a phenol ring introduced into the polyester resin.